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Old 06-22-2014, 03:23 AM   #1 (permalink)
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single point threads

I figured this would be the best place to ask. I've been learning how to thread on my lathe but having trouble getting good results. I Rethreaded a traccer body to cocker threads but when I checked the fit with a stiffi barrel it got stuck and galled leaving parts of the barrel threads in the body.

When I checked the thread size and compared it to the other 3 barrels I have it was the biggest one. What would I clean up the new threaded section with? Do I make the threads and then bore it to final minor dia to knock down super sharp threads?

I need help.

Last edited by kit; 07-01-2014 at 04:24 AM.
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Old 06-24-2014, 11:13 PM   #2 (permalink)
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The best thing I found to do specifically for ID threads but works on all. Make or use a gauge. The gauge can be a real go/nogo gauge or just the part you want to fit. Thread to just about 0.005 under size mathematically then start using your gauge take a cut test the fit take a cut test the fit just keep going like that until it feels right.
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Old 06-24-2014, 11:22 PM   #3 (permalink)
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my personal favourite approach is to use crest-topping inserts as often as realistically possible, including on manual jobs. produces a cleaner, more accurate thread, with the final size on the "top" of the thread (minor or major diameter depending on internal/external) and the pitch diameter being produced at the same time, with no worries about having to clean up the top of the thread.

if you don't have access to crest top threading tools or inserts, your best approach for clean threads is going to be using the sharpest tools possible with geometry appropriate to the material (aluminum presumably in this case). beyond that, and using material-appropriate cutting oil (A-1 is what I'd recommend), there are a couple approaches to cleaning up the threads, either by moving the compound back and forth to cut only one side of the thread at a time, or the 29 degree method which I haven't used in about 10 years but I recall it producing good results.
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Old 06-25-2014, 05:17 PM   #4 (permalink)
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Thanks for the reply. I have the 7x12 mini lathe so I can't chuck the piece as close as I would like. It only has a 3/4in thru hole. I had to clamp down where the body has the slot. Even with a plug I inserted in the body, I didn't want to wrench down on the chuck. I was getting a bit of chatter when I did the spring cuts.

Maybe my bit isn't sharp enough( hss tool bits I ground on the grinder to make the 60 degree bit.) I also don't have my compound at 29 degrees, I just advance in with the cross slide. I also don't have cutting oil or used any.

I'll try the suggestions on the other body I have. I did the go- no go with the barrels I had and the brass one went in fine. That's when the stiffi got stuck and I had to work on it to get it off and found all the barrels was a bit different. The stiffi was largest by far.
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Old 06-30-2014, 05:41 PM   #5 (permalink)
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The way you are advancing the cutting tool into the part will cause a lot of chatter, try the 29* method, forming only one side of the thread cuts much smoother. I also recommend some sort of cutting fluid, I use Rapid Tap and get decent results on aluminum and stainless with it.

Autococker barrel threads have changed over the years, really old barrels wont fit new bodies and viceversa. I wish I had a standard size to give for the threads, I think its 15/16"-20.

Also try regrinding your threading tool, make your cutting edge sharper like a blade. Aluminum likes to cut not tear like steel does, a sharp and well polished tool should help a bit.
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Old 06-30-2014, 05:45 PM   #6 (permalink)
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When you are chucking up parts remember the 4xD rule of thumb. You can have 4 times the diameter of the part sticking out of the jaws before you get lots of deflection.
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Old 06-30-2014, 05:58 PM   #7 (permalink)
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Almost sounds like your threads weren't quite deep enough.

Here's some good info on cocker threading.
Making a standard thread for all Paintball Guns... "Autococker".

Originally Posted by senghing27
Note: While I would love to take credit for his work, I am not associated with Mad Customs!
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Old 07-01-2014, 03:18 AM   #8 (permalink)
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I'm probably doing everything all wrong. I don't even have a threading gauge to line up my tool bit to the part or thread pitch gauge to check my work. But I was able to clean up the traccer body threads and even got the stiffi barrel to fit.

I got lazy and didn't machine my boring bar to fit the tool holder so I just clamp it on to bore out the pump handle

Got it together with a brass barrel.

I'm now trying to make a body from scratch out of magnesium. Threaded the front for the barrel, now need to figure out how to bore the hole for the guts with my tiny lathe.

Hope the pictures work.

Last edited by kit; 07-01-2014 at 03:47 AM.
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